This invention is concerned with the field of light energy concentrating devices. More specifically, this invention is related to devices comprising a plurality of segments which are capable of reflecting light and which are pivotable in unison about two axes in order to direct light, emanating from a moving source, to a focal region.
Although the relatively recent realization of the possibility of severe energy shortages has been a motivating force for research and development in the field of solar energy concentrating devices, the art of using devices for such a purpose is quite old. Indeed, years ago scientists discovered that certain devices were better suited for concentrating energy than others. Many solar energy concentrating devices which have been proposed utilize a system of reflective surfaces to focus or concentrate light onto a receiver. For example, U.S. Pat. Nos. 1,951,404, 3,254,207, 4,088,121, and 4,147,414 disclose such devices.
It has long been known that a parabolically shaped reflector can be used to concentrate light beams on the focus of the parabola. A parabola, in mathematical terms, is the locus of points which lie in a plane equidistant from a given point, called the focus, and a given line, called the directrix. Thomas, Jr., George B., CALCULUS AND ANALYTIC GEOMETRY, Addison-Wesley Publishing Co., Inc., 1965, 3rd Edition, P. 465. The unique geometry of a parabola results in rays of light coming into the parabola at an angle perpendicular to the directrix (parallel to the axis of the parabola), being concentrated at the parabola's focus. This occurs assuming the correctness of the optical relationship such that the angle of reflection of a ray of light striking a mirror is equal to the angle of incidence.
Although these fundamental geometrical and optical relationships have been known for quite some time, a relatively simple, easily built and easily maintained device for effectively and efficiently concentrating solar energy has eluded the art. This is not to suggest that solar energy devices attempting to exploit the advantageous geometrical relationships of parabolas have not been considered. Quite to the contrary, such devices have apparently been considered by practitioners in the art, but because of practical considerations these devices have apparently not been universally accepted.
There are several examples of solar energy concentrating devices disclosed in Jan. F. Kreider et al.'s SOLAR HEATING AND COOLING, Engineering, Practical Design and Economics, revised first edition, Hemisphere Publishing Corp., 1977. For example, on page 82 of that book it is disclosed that a large parabolic mirror was used in 1878 to focus solar rays onto an absorber placed at the parabola's focus. Also disclosed on that same page of the book is a trough-type parabolic reflector which was movable to maintain the sun's rays perpendicular to the directrix of the parabola. In that device, a tubular absorber was placed along the parabola's focus in order to receive the concentrated sunlight.
Kreider's book (on page 83) also discloses several relatively new solar concentrating devices which provide for solar concentration without the need of moving the reflectors. One of the devices, called SRTA (stationary reflector/tracking absorber), apparently utilizes a fixed parabolically shaped reflector and a movable absorber. Another device, called CPC (compound parabolic concentrator), was developed by Roland Winston at Argonne National Laboratory, Argonne, Illinois, and consists of two sections of a parabola which form a trough-like solar concentrator.
Even with the development of these devices, there still appears to be a need for a rather simple, efficient and economic device for concentrating light.